Bishop Ivo Lorscheiter

The Brazilian Bishop Jose Ivo Lorscheiter, who has died aged 79, was a leading proponent of liberation theology and renowned for denouncing torture and human rights abuses by his country's military rulers during the 1964 regime.

But he consistently played down his actions during what are known in Brazil as the anos de chumbo or "heavy years". Facing up to the dictatorship was, he argued, merely his obligation as a Christian. "For me these difficulties were normal," he once said. "As a Christian, it was my duty to defend human rights. I always felt that the people trusted in our actions and I was never reticent."

Lorscheiter was born in Sao Jose do Hortencio, in the southern state of Rio Grande do Sul. Part of a long tradition of south American Catholic leaders who promoted social, economic and political justice in one of the world's most unequal societies, he was one of seven brothers born to rural farmers. Like many in the region, his parents were descendants of German immigrants. Their real surname was Lorscheider, but an error at the register office meant that the bishop's name was misspelt throughout his life.

Lorscheiter, or "Dom Ivo" as followers would later call him, began his trajectory within the Catholic church at the age of 12, when his father decided he should attend the local seminary. He went on to study theology in Rome, and in 1952 returned to Brazil. In 1965 he took over as auxiliary bishop in the southern city of Porto Alegre.

This was a turbulent time in Brazilian history. The previous year, a military dictatorship had taken hold of the country and begun to hunt down all those who opposed its hardline policies. Brazil's dictators never earned the notoriety of their Argentinian counterparts, who are believed to have killed up to 30,000 opponents between 1976 and 1983. Nevertheless, hundreds of Brazilian dissenters disappeared at the hands of the army, while many others were unjustly imprisoned or tortured.

Despite the risks, Lorscheiter did not shy away from criticising the regime that ruled Brazil from 1964 to 1985. Between 1971 and 1979, he served as secretary-general of Brazil's bishops' conference, where he gained a reputation as a progressive leader with a strong commitment to the country's impoverished masses. In 1974, he was nominated as bishop of Santa Maria, and in 1979 he became the conference's president, a role he fulfilled until 1987.

From 1970 to 1974, Lorscheiter also took part in secret negotiations between members of the Catholic church and the military rulers. He repeatedly clashed with the dictatorship, helping to track down political prisoners and championing the cause of hundreds of desaparecidos, the political activists and leftwing guerrillas who went missing after challenging the regime.

Lorscheiter was famed for daring to stand up to the military leaders at a time when many preferred to remain silent. "You do things that are morally unjust," he once reportedly told the hardline president General Emilio Medici. "We had to oppose [the regime]," he said in a 2002 interview. "Absolutely anyone was being called subversive."

Lorscheiter's commitment to liberation theology meant he was often at odds with the Vatican, particularly after the accession in 1978 of the conservative Pope John Paul II, who was famed for opposing the involvement of south American Catholic leaders in liberation theology.

Health problems plagued Lorscheiter throughout his life and in recent years he was repeatedly admitted to hospital. He retired in 2004, becoming an emeritus bishop. Around 5,000 followers attended his funeral and three days of official mourning were announced. President Luiz Inacio Lula da Silva, who was himself imprisoned by the military dictatorship, described Lorscheiter as a "marvellous human being, who leaves us all an example for life and dedication to good causes".

· Jose Ivo Lorscheiter, cleric, born December 7 1927; died March 5 2007